Actually, after looking at it even more it seems too white to be old. It could be off a modern day elephant. Do you have a microscope? If you do you would be able to put it under the microscope and it you can see grains of sand or something like that it is a subfossil. Woolly mammoth fossils are not fossils-they are usually sub-fossils. Here is one of many mammoth teeth in my collection. It looks identical, appart from it is darkest in colour. For your tooth, I can't tell if it is from a mammoth, a mastodon or an elephant, but I can garuntee it is off something related to an elephant, if not an elephant.